I usually turn off cast shadow for hair because when I don't, I often end up with ugly black patches instead of subtle shadows... especially at the neck area. To me a shadow should be darker, but still allow you to see the shape of what is there. I never get that when I have hair casting shadows....just plain opaque ugly black voids.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi